Mercury switch having at least one contact preformed from an alloy containing nickel,copper and tin



Jan. 20, 1970 M BARLQW ET AL 3,491,219

MERCURY SWITCH HAVING AT LEAST ONE CONTACT PREFORMED 5 FROM AN ALLOY CONTAINING NICKEL, COPPER AND TIN Filed Dec. 27, 1968 2 Sheets-Sheet 1 FIG.

lNVE/VTORS M. BARLOW P. J. PLANT/N6 BY A T TORNEV Jan. 20, 1970 Flled Dec 27, 1968 M. BARLOW ETAL 3,491,219 MERCURY SWITCH HAVING'AT LEAST ONE CONTACT PREFORMED FROM AN ALLOY CONTAINING NICKEL, COPPER AND TIN 2 Sheets-Sheet 2 60% NICKEL 35% COPPER 5%TIN CONTACT OPERATIONS q O O O O O no w m 5 4 3 2 m 8 5 hzwmmau wmxfidm Q24 whqmwao zmmtshwm wuzmmmfiio United States Patent O 3,491,219 MERCURY SWITCH HAVING AT LEAST ONE CON- TACT'PREFORMED FROM AN ALLOY CONTAIN- ING NICKEL, COPPER AND TIN Malcolm Barlow and Peter J. Planting, Sunnyvale, Calif., assign'ors to Bell Telephone Laboratories, Incorporated, Murray Hill, N.'J., a corporation of New York Confinuafion-in-part of application Ser. No. 620,388, Mar. 3, 1967. This application Dec. 27, 1968, Ser. -No.'787,472

Int. Cl. H01h 3/00, 9/00 US. Cl. 200-166 6 Claims ABSTRACT OF THE DISCLOSURE A sealed contact switching dew'ce having'contacts wetted by mercury is disclosed in which the mercury includes a copper additive and at least one contact surface is preformed from an alloy containing various percentages of nickel, copper and tin.

This application is a continuation-in-part of our copending application Ser. No. 620,388, new Patent No. 3,431,377, and refers to electrical switches in which mercury is used on the contacting surfaces to improve performance, i.e., mercury switches.

Heretofore, many mercury switches used a contact material consisting of pure platinum or an alloy of platinum and nickel. While that contact material generally gave good results, the contacts tended to stick during operation. While 'the'tendency to stick can be reduced by changing the constituents of the contact material, such changes often produce unstable operation. That is, contact materials which reducethe tendency of the contacts to stick often exhibit a changing difference between the magnitud'e's of operating and release currents as the number of operations increases. When a mercury switch manifests such changes, it is generally considered to be unstable.

Accordingly, it is broadly the object of this invention to stabilize the difiere'nce between operate and release currents in sealed contact switching devices using mercury to wet the contact surfaces.

SUMMARY OF THE INVENTION DESCRIPTION OF THE DRAWING FIG. 1 illustrates in partial section view a sealed contact switch containing at least one preformed contact and containing a mercury solution for wetting the surface of the contacts;

FIG. 2 is a graph of experimental data comparing the stability of operation of a switch having contacts preformed from an alloy containing nickel, copper and tin with the stability of operation of a switch having contacts preformed from an alloy containing only nickel and copper.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, the illustrated switch comprises an envelope or housing which may be made of 3 ,4 91 ,Z l 9 Patented Jan. 20, 1970 glass and which has two ends 10a and 101.). Two opposed pole piece terminals 11 and 12 are sealed in the end 10a. Both terminals are made from magnetic material such as 52 Alloy. "52 Alloy is a composition consisting essentially of 52 percent nickel and 48 percent iron. Further, the facing ends of each terminal 11 and 12 are provided with a contact 13 and 14, respectively. The composition of the contacts '13 and 14 is described below in detail.

A metal tube 20 is sealed in the end 101; so as to extend into the housing 10.One part of the tube 20 is located within the envelope and has a flared or cup-like portion 20a for holding an electrically conducting contact wetting liquid, viz, mercury 21. As illustrated, the -mercury 21 is present in a quantity sufficient to fill part of the housing 10 and cover the cup-like portion 20a. Furthermore, while the mercury 21 can be essentially pure, it may also be saturated with a copper additive such as by welding a piece of oxygen-free, high conductivity copper wire to, for example, the tube 20 so that it will be immersed in the mercury 21 when the switch is assembled.

A reed or swinger 15 is secured to the cup 20a. It is madeof a-rnagnetic material such as 78.5 Permalloy. 78.5 Permalloy is a composition consisting essentially of 21.2 percent iron, 78.5 percent nickel and .3 percent manganese. One end of the swinger 15 terminates in a contacting portion 15a and the other end terminates in a looped portion 15b. The central portion of the swinger -15 is adapted to transport the mercury 21 readily between the portions 15a and 15b. The looped portion 15b contacts the mercury 21 in the cup 20a and the contacting portion 15a is wetted by the mercury 21 transported by the central portion of the swinger 15. Finally, the contact portion 15a is disposed between the terminals 11 and 12 in a position to readily engage the contacts 13 and 14.

An energizing coil 22 shown schematically in the drawing surrounds the housing 10.

The theory of operation of mercury contact switches is well known 'to those skilled in the art and, accordingly, it is not discussed. For further information regarding the particular type of switch chosen to illustrate this invention, reference is made to US. Patents 2,609,464 and 2,868,926 issued to J. T. L. Brown et all. and C. E. Pollard, In, respectively. Generally, however, the swinger 15 reciprocates between the contacts 13 and 14 in response to 'energization of the coil 22. Switching occurs when the swinger 15 engages one of the contacts through the mercury 21.

The contact 13, the contact 14 and, if desired, the contacting portion 15a of the swinger 15 which engages the contacts 13 and 14 are preformed of an alloy before asse'rnbly in the switch. Specifically, they are preformed from an alloy which is substantially nonmagnetic, which will not amalgamate in bulk with the wetting agent (viz, the mercury 21) and only slightly, if at all, on the surface, and which will form an advancing contact angle with the wetting agent of 20 degrees or less. For the purposes of this description, an advance contact angle is defined as the angle lying between a surface being wetted and a plane lying tangent to the leading edge of the medium which is wetting the surface.

In order to improve stability between operating and release currents, the alloy from which the contacts are preformed consists of copper, nickel and a small amount of tin. For example, the alloy in the particular embodiment being described consists of copper, nickel and tin mixed in the proportions by weight of copper, 35 percent; nickel, 60 percent; and tin, 5 percent. In addition, the mercury 21 is advantageously saturated with a copper additive.

The performance of switches having preformed contacts made of an alloy of this type and using mercury containing a copper additive as the wetting agent has been measured and compared with the performance of switches having preformed contacts made of another alloy (viz, nickel and copper alone). From the results, the former demonstrate a substantial improvement in stability over the latter.

FIG. 2 summarizes the results of those tests; that is, FIG. 2 plots test data on an ordinate which is divided into milliamperes and an abscissa which is divided into numbers of contact operation. The steeper or upper curve passes through values of operate and release current measured at increasing numbers of Operation in a switch using a preformed contact made of an alloy containing 57 percent nickel and 43 percent copper by weight and using mercury containing copper additives as a contact wetting agent. The flatter or lower curve, on the other hand, passes through similar values obtained from a switch in which the contacts are preformed from an alloy containing 60 percent nickel, 35 percent copper and 5 percent tin by weight and using mercury containing copper additives as the wetting agent; The table below sets forth illustrative test measurements of operating and release current.

Difierence between operate and release currents (milllamps) (alloy) Number of operations (millions) 67% Ni, 43% Cu 60% Ni, 35% Cu, 5% S11 In the relays tested, the contacts 13 and 14 were preformed from a combination consisting of a base metal and an alloy formed by melting together nickel, copper and tin in the proportions of 60 percent nickel, percent copper and 5 percent tin by Weight. With a fused alloy of this type, the contacts 13 and 14 are readily made by bonding a sheet of the alloy over the base metal and then stamping or cutting out contacts from the composite structure. The resulting contacts-will have a base metal suitable for joining to one of the terminals 11 or 12 and a contact surface adapted to engage the swinger 15 and be wetted by the mercury 21.

Other ways of making the contacts 13 and 14 are also feasible. For instance, they can be formed by sputtering or by electroplating the alloy metal over the base metal. Whichever method is used, however, the alloy metal overlay in the preformed contact should have a thickness on the order of 10 microns or greater.

The respective proportions of copper, nickel and tin in the alloy can usefully be varied. While in the particu lar embodiment illustrated herein, nickel, copper and tin are present in specific proportions, other proportions will also provide good results. For example, where a high level of stability is not of the utmost importance, the percentages of nickel, copper and tin can fall in the ranges 50 percent to 70 percent, 25 percent to 49 percent, and 1 percent to 5 percent, respectively, by weight. But better 4 results are achieved where the percentage of nickel falls within the range of percent to 65 percent by weight and the percentage of copper falls within the range of 30 percent to 44 percent by weight. The best results, however, are achieved Where the ranges are, by weight, percent to 62.5 percent nickel, 35 percent to 36.5 percent copper and 1 percent to 5 percent tin.

In summary, a switching device containing contacts wetted by an electrically conducting agent has been disclosed in which the difference between operating and release currents is stabilized over a substantial number of operations. It is to be understood, however, that the above described arrangements are merely illustrative of the application of the principles of this invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. In a sealed contact switching device containing a contact wettable by mercury, the combination comprisa first contact having a surface preformed from an alloy consisting of nickel, copper and tin;

a second contact for engaging said first contact; and

mercury wetting the contacting portions of said first and second contacts.

2. The combination in accordance with claim 1 wherein the percentage of tin in said alloy ranges from 1 percent to 5 percent by weight.

3. The combination in accordance with claim 1 wherein the percentage'of nickel in said alloy ranges from 50 percent to 70 percent by weight and the percentage of copper ranges from 25 percent to 49 percent by weight.

4. The combination in accordance with claim 1 wherein the percentage of nickel in said alloy ranges from 55 percent to percent by weight and the percentage of copper ranges from 30 percent to 44 percent by Weight.

5. The combination in accordance with claim 1 wherein the percentage by weight of nickel in said alloy ranges from 60 percent to 62.5 percent and the percentage by weight of copper in said alloy ranges from 36.5 percent to 39 percent.

6. The combination in accordance with claim 1 wherein the percentage of nickel in said alloy is 60 percent by weight, the percentage of copper in said alloy is 35 percent by weight, and the percenatge of tin in said alloy is 5 percent by weight.

References Cited UNITED STATES PATENTS 2,769,875 11/1956 Brown et al. 2,868,926 1/1959 Pollard 335-55 3,018,354 l/1962 Pollard. 3,054,873 9/1962 OBrien et al. 335 -55 X 3,146,328 8/1964 Mason et al. 3,344,373 9/1967 Janninck 33555 X 3,431,377 3/1969 Barlow et al.

HERMAN O. JONES, Primary Examiner 

